TETRA is a modern standard for digital Private Mobile Radio (PMR) and Public Access Mobile Radio (PAMR). It offers many advantages including flexibility, security, ease of use and offers fast call set-up times. This makes it an ideal choice for many business communications requirements.

The name TETRA stands for TErrestrial Trunked RAdio. Aimed at a variety of users including the police, ambulance and fire services, it is equally applicable for utilities, public access, fleet management, transport services, and many other users. It offers the advantages of digital radio whilst still maintaining the advantages of a PMR system.

Tetra radio beginnings
Work started on the development of the TETRA standards in 1990 and has relied on the support of the European Commission and the ETSI members. Experience gained in the development of the highly successful GSM cellular radio standard, as well as experience from the development and use of trunked radio systems has also been used to fashion the TETRA standard. In addition to this the process has gained from the co-operation of manufacturers, users, operators and industry experts. With this combined expertise the first standards were ready in 1995 to enable manufacturers to design their equipment to interoperate successfully.

Tetra radio features
TETRA radio offers many new and valuable features. These include a fast call set-up time, which is a particularly important requirement for the emergency services. It also has excellent group communication support, direct mode operation between individual radios, packet data and circuit data transfer services, better economy of frequency spectrum use than the previous PMR radio systems and in addition to this it provides advanced security features. The system also supports a number of other features including call hold, call barring, call diversion, and ambience listening.

The TETRA radio system uses Time Division Multiple Access (TDMA) technology with 4 user channels on one radio carrier and 25 kHz spacing between carriers. This makes it inherently more efficient than its predecessors in the way that it uses the frequency spectrum. Data can be transmitted at 7.2 kbits per second for a single channel. This can be increased four fold to 28.8 kbits per second when multi-slot operation is employed.

For emergency services in Europe the frequency bands 380-383 MHz and 390-393 MHz have been allocated. These bands can be expanded to cover all or part of the spectrum from 383-395 MHz and 393-395 MHz should this be needed. For civil systems in Europe the frequency bands 410-430 MHz, 870-876 MHz / 915-921 MHz, 450-470 MHz, 385-390 MHz / 395-399,9 MHz, have been allocated.

TETRA radio trunking facility provides a pooling of all radio channels that are then allocated on demand to individual users, in both voice and data modes. By the provision of national and multi-national networks, national and international roaming can be supported, the user being in constant communication. TETRA supports point-to-point, and point-to-multipoint communications both by the use of the TETRA infrastructure and by the use of Direct Mode without infrastructure.

In addition to this it is possible for TETRA radio to operate in a secure format. The digital data can be encrypted before transmissions, making the system inherently secure. This may be required for some covert operations or for the police services.

TETRA radio operation
There are three different modes in which TETRA can be run:

* Voice plus Data (V+D)


* Direct Mode Operation (DMO)


* Packet Data Optimised (PDO)


The most commonly used mode is V+D. This mode allows switching between speech and data transmissions, and can even carry both by using different slots in the same channel. Full duplex is supported with base station and mobile radio units frequencies normally being offset by about 10 MHz to enable interference levels between the transmitter and receiver in the station to be reduced to an acceptable level.

DMO is used for direct communication between two mobile units and supports both voice and data, however full duplex is not supported in this mode. Only simplex is used. This is particularly useful as it allows the mobile stations to communicate with each other even when they are outside the range of the base station.

The third mode, PDO is optimised for data only transmissions. It has been devised with the idea that much higher volumes of data will be needed in the future and it is anticipated that further developments will be built upon this standard.

Data structures
TETRA radio uses TDMA techniques. This enables much greater spectrum efficiency than was possible with previous PMR systems because it allows several users to share a single frequency. As the speech is digitised, both voice and data are transmitted digitally and multiplexed into the four slots on each channel. Digitisation of the speech is accomplished using a system that enables the data to be transmitted at a rate of only 4.567 kbits/second. This low data rate can be achieved because the process that is used takes into account the fact that the waveform is human speech rather than any varying waveform. The digitisation process also has the advantage that it renders the transmission secure from casual listeners. For greater levels of security that might be required by the police or other similar organisations it is possible to encrypt the data. This would be achieved by using an additional security or encryption module.

The data transmitted by the base station has to allow room for the control data. This is achieved by splitting what is termed a multiframe lasting 1.02 seconds into 18 frames and allowing the control data to be transmitted every 18th frame. Each frame is then split into four time slots. A frame lasts 56.667 mS. Each time slot then takes up 14.167 mS. Of the 14.167mS only 14 milliseconds is used. The remaining time is required for the transmitter to ramp up and down. The data structure has a length of 255 symbols or 510 modulation bits. It consists of a start sequence that is followed by 216 bits of scrambled data, a sequence of 52 bits of what is termed a training sequence. A further 216 bits of scrambled data follows and then the stream is completed by a stop sequence. The training sequence in the middle of the data is required to allow the receiver to adjust its equaliser for optimum reception of the whole message.

The data is modulated onto the carrier using differential quaternary phase shift keying. This modulation method shifts the phase of the RF carrier in steps of ± pi /4 or ±3 pi /4 depending upon the data to be transmitted. Once generated the RF signal is filtered to remove any sidebands that extend out beyond the allotted bandwidth. These are generated by the sharp transitions in the digital data. A form of filter with a root raised cosine response and a roll off factor of 0.35 is used. Similarly the incoming signal is filtered in the same way to aid recovery of the data.

Additionally, TETRA radio uses error tolerant modulation and encoding formats. The data is prepared with redundant information that can be used to provide error detection and correction. The transmitter of each mobile station is only active during the time slot that the system assigns it to use. As a result the data is transmitted in bursts. The fact that the transmitter is only active for part of the time has the advantage that the drain on the battery of the mobile station is not as great as if the transmitter was radiating a signal continuously. The base station however normally radiates continuously as it has many mobile stations to service.

One important feature of TETRA is that the call set up time is short. It occurs in less than 300 mS and can be as little as 150 mS when operating in DMO. This is much shorter than the time it takes for a standard cellular telecommunications system to connect. This is very important for the emergency services where time delays can be very critical.

Further TETRA radio developments
While TETRA radio is a major improvement over the previous PMR systems in operation, additional data capacity is always needed. In view of the higher data capabilities now being offered by the cellular services, the TETRA radio standard is being updated to enable it to keep pace with other comparable technologies. In this way, TETRA will be able to offer commercial users the advantages of a PMR service alongside the data capabilities of a cellular network. Read more....!

A trunked version of the Private Mobile Radio (PMR) concept that is defined under the standard MPT 1327 (MPT1327) is widely used and provides significant advantages over the simpler single station systems that are in use. MPT1327 enables stations to communicate over wider areas as well as having additional facilities.

In view of the very high cost of setting up trunked networks, they are normally run by large leasing companies or consortia that provide a service to a large number of users. In view of the wider areas covered by these networks and the greater complexity, equipment has to be standardised so that suppliers can manufacture in higher volumes and thereby reduce costs to acceptable levels. Most trunked radio systems follow the MPT1327 format.

To implement trunked PMR a network of stations is set up. These stations are linked generally using land lines, although optical fibres and point to point radio are also used. In this way the different base stations are able to communicate with each other.

In order to be able to carry the audio information and also run the variety of organisational tasks that are needed the system requires different types of channel to be available. These are the control channels of which there is one in each direction for each base station or Trunking System Controller (TSC).

A number of different control channels are used so that adjacent base stations do not interfere with one another, and the mobile stations scan the different channels to locate the strongest control channel signal. In addition to this there are the traffic channels. The specification supports up to 1024 different traffic channels to be used. In this way a base station can support a large number of different mobile stations that are communicating at the same time. However for small systems with only a few channels, the control channel may also act as a non-dedicated traffic channel.

The control channels use signalling at 1200 bits per second with fast Frequency Shift Keying (FFSK) subcarrier modulation. It is designed for use by two-frequency half duplex mobile radio units and a full duplex TSC.

For successful operation it is essential that the system knows where the mobiles are located so that calls can be routed trough to them. This is achieved by base stations polling the mobile stations using the control channel.

To make an outgoing call the mobile transmits a request to the base station as requested in the control channel data stream from the base station. The mobile transmits its own code along with that of the destination of the call, either another mobile or a control office. The control software and circuitry within the base station and the central control processing area for the network sets up the network so that a channel is allocated for the audio (the traffic channel). It also sets up the switching in the network to route the call to the required destination.

To enable the mobile station to receive a call, it is paged via the incoming control channel data stream to indicate that there is an incoming call. Channels are allocated and switching set up to provide the correct routing for the call.

There is no method to "handover" the mobile from one base station to the next if it moves out of range of the base station through which a call is being made. In this way the system is not a form of cellular telephone. It is therefore necessary for the mobile station to remain within the service area of the base station through which any calls are being made.

The control channel signalling structure has to be defined so that all mobiles know what to expect and what data is being sent. Signalling on the forward control channel is nominally continuous with each slot comprising 64 bit code words. The first type is the Control Channel System Codeword (CSCC). This identifies the system to the mobile radio units and also provides synchronisation for the following address codeword. As mentioned the second type of word is the address codeword. It is the first codeword of any message and it defines the nature of the message. It is possible to send data over the control channel. When this occurs, botht he CSCC and the address codewords are displaced with the data appended to the address codeword. The mobile radio unit data structure is somewhat simpler. It consists fundamentally of synchronism bits followed by the address codeword.

There are a number of different types of control channel messages that can be sent by the base station to the mobiles:

Aloha messages -- Sent by the base station to invite and mobile stations to access the system.

Requests -- Sent by radio units to request a call to be set up.

"Ahoy" messages -- Sent by the base station to demand a response from a particular radio unit. This may be sent to request the radio unit to send his unique identifier to ensure it should be taking traffic through the base station.

Acknowledgements -- These are sent by both the base stations and the mobile radio units to acknowledge the data sent.

Go to channel messages -- These messages instruct a particular mobile radio unit to move to the allocated traffic channel.

Single address messages -- These are sent only by the mobile radio units.

Short data messages -- These may be sent by either the base station or the mobile radio unit.

Miscellaneous messages -- Sent by the base station for control applications.

One of the problems encountered by mobile signalling systems is that of clashes when two or more mobile radio units try to transmit at the same time on the control channel. This factor is recognised by the system and is overcome by a random access protocol that is employed. This operates by the base station transmitting a synchronisation message inviting the mobile radio units to send their random access message. The message from the base station contains a parameter that indicates the number of timeslots that are available for access. The mobile radio unit will randomly select a slot in which to transmit its request but if a message is already in progress then it will send its access message in the next available slot. If this is not successful then it will wait until the process is initiated again.

Although the data is transmitted as digital information, the audio or voice channels for the system are analogue, employing FM. However some work has been carried out to develop completely digital systems. The main systems are by Motorola, by Ericsson (EDACS) and Johnson (LTR). These systems have not gained such widespread acceptance. Read more....!

Private Mobile Radio (PMR) or as it is sometimes called Professional Mobile Radio is widely used for businesses as a very convenient way of communicating. The basic concept has been in use for many years and was firmly established prior to the introduction of the first cell phone systems, although systems including MPT1327 that provide trunking and TETRA enable far greater facilities.

The first PMR systems were initially set up to enable a set of mobile business users to maintain contact with a base. Organisations such as taxi firms, utility workers and the like all used these systems as they enabled them to maintain contact with their office. Additionally the emergency services used their own systems.

Initially the systems consisted of a base station with a number of mobile stations. Communication used a single frequency, with simplex push to talk transmissions. As pressure rose on the frequency allocations, often frequencies had to be shared. As the systems almost invariably used frequency modulation, squelch was employed so that the audio from the received was only switched on when a signal was present. Developments of this known as DTMF (dual tone multiple frequency) and CTCSS (continuous tone, coded squelch system) were used to enable only the required users to hear the call.

These systems were only able to communicate over relatively short distances. They used a single central base station to communicate with all the mobile stations. This considerably reduced their coverage area. To overcome this a system known as trunking was devised whereby several transmitters could be used and the signal was “trunked” to the correct station. Several systems are available for this but the one that has gained by far the widest use is specified as MPT 1327.

All the standards mentioned so far are analogue systems. The cellular telecommunications industry moved to digital technology to provide improved efficiency of spectrum usage along with a variety of new facilities. So too did the PMR industry with the induction of a system known as TETRA. . Originally the letters stood for Trans European Trunked RAdio, but as the system is now being used beyond Europe the abbreviation now stands for TErrestrial Trunked RAdio. This system provided a far more flexible service along with all the other advantages of using a digital system. Read more....!

Digital Multimedia broadcasting, DMB is based on the Eureka 147 Digital Audio Broadcast or DAB system that is widely deployed in the UK and many other countries around the world for audio broadcasting. One of the advantages of using DMB is that it can be rolled out and used without much modification for mobile video applications, simply increasing the level of error correction to cope with the mobile environment.

In view of the different broadcasting platforms that could be used account needs to be taken of this. Eureka 147 allows for broadcasts both from terrestrial transmitters and from satellite based transmitters. For DMB both platforms are possible, but in view of the differing platforms and transmission requirements there would need to be some modifications between the two systems. For terrestrial based transmissions a flavour of the system designated as T-DMB (Terrestrial Digital Multimedia Broadcasting) is used, whereas for satellite broadcasting S-DMB (Satellite Digital Multimedia Broadcasting) is used.

RF signal characteristics
Like many other broadcasting systems, DMB and DAB use a form of transmission known as Orthogonal Frequency Division Multiplex (OFDM). This has been adopted because of its high data capacity and suitability for applications such as broadcasting. It also offers a high resilience to interference, can tolerate multi-path effects and is able to offer the possibility of a single frequency network, SFN.

DMB format
The transmissions for the form of DMB being deployed in many countries occupy approximately 1.5 MHz bandwidth and for the VHF broadcasts the transmission contains 1536 Carriers. However it is possible to use a variety of modes:

* 2K mode 1536 carriers

* 1K mode 768 carriers

* 0.5K mode 384 carriers

* 0.25K mode 192 carriers

Frequency allocations
It would be possible to utilise the DAB transmission system within the UK for DMB, however much of the capacity has been taken up, although some reserve capacity has been retained for future data transmissions of which DMB could be part.

A more likely solution for DMB is to use frequencies within the L-Band DAB allocation (1452 - 1467.5 MHz). This might be possible in some countries where the use of this broadcasting allocation could be used for this purpose with little legislation.

Using a new band it will not only be possible to use smaller antennas, an important element for mobile phones and PDAs, but it will also be possible to tailor the transmission to accommodate the Doppler shifts likely to be encountered by small mobile devices. This can be achieved by reducing the number of carriers. Despite the carrier number reduction, the maximum data rate of 1.152 Mbps is still retained. The drawback of using the L band frequencies is that they would require a much higher density of transmitters to provide the required coverage.

Battery consumption
One of the major requirements for any mobile video system such as DMB is that it shall not place a major load on the battery of the handheld device. With user expectations requiring that battery life shall be several days between recharges, this is a major consideration. While battery technology is improving, and IC technology has enabled current consumption of chips to be reduced, the basic technology can also play its part.

DMB is also ideally suited to the delivery of material to handheld devices. DAB inherently includes a technique known as time slicing by using an effectively using a Time Division Multiplexing delivery method. In this way the receiver is only switched on when it is required, thereby saving battery power.


It remains to be seen whether DMB or DVB-H will be the major standard that is adopted for mobile video. Some indicate that both schemes may be used in different countries around the world Accordingly many chip manufacturers whoa re addressing this market are catering for both schemes and developing systems that will be able to switch between the variety of bands that will be used around the globe.

In addition to this DMB trials are well advanced, particularly in Korea where it appears DMB will be adopted. For other countries, it remains to be seen what happens. Read more....!

DVB-H or Digital Video Broadcast - Handheld, is one of the major systems to be used for mobile video and television for cellular phones and handsets. DVB-H has been developed from the DVB-T (Terrestrial) television standard that is used in many countries around the globe including much of Europe including the UK, and also other countries including the USA. The DVB-T standard has been shown to be very robust and in view of its widespread acceptance it forms a good platform for further development for handheld applications.

DVB-H development requirements
The environment for handheld devices is considerably different to that experienced by most televisions. Normally domestic televisions have good directional antenna systems and in addition to this the reception conditions are fairly constant. Additionally most televisions receiving DVB-T will be powered by mains supplies. As a result current consumption is not a major issue.

The conditions for handheld receivers are very different. In the first instance the antennas will be particularly poor because they will need to be small, and integrated into the handset in such a way that they either appear fashionable, or they are not visible. Additionally they will obviously be mobile, and this will entail receiving signals in a variety locations, many of which will not be particularly suitable for video reception. Not only will be signal be subject to considerable signal variations and multi-path effects, but it may also experience high levels of interference. Also some difficulties are presented by the fact that the handset could be in a vehicle and actually on the move. The operation of DVB-H has to be sufficiently robust to accommodate all these requirements.

"Note on multi-path effects:

Multi-path effects occur when signals reach the receiver via several different paths from the transmitter. This occurs because the signals leave the transmitter in a variety of directions - typically the transmitter may have an omni-directional radiation pattern so that it radiates signals equally in all directions. Accordingly some of the signal may travel directly to the receiver in what is termed the direct path, but some of the radiated may be reflected off a nearby hill, building or other object. In fact the received signal will consist of components reaching the receiver from the transmitter via a large number of paths. As the path length travelled by each of these components will be slightly different, each component will arrive at a slightly different time. If there are significant differences, this can cause the data being transmitted to be corrupted under some circumstances, although many modern receiver technologies can accommodate this and use the different signals travelling over different paths to reinforce one another."

While DVB-T proved to be remarkably robust under many circumstances, one of the major problems was that of current consumption. Battery life for handsets is a major concern where users anticipated the life between charges will be several days.

Operation of DVB-H
The DVB-H standard has been adopted by ETSI, European Telecom Standards Institute, and in this way the system can be truly international, and this will prevent compatibility problems caused by different countries and operators using different variants of the same system. The documents for the physical layer were ratified in 2004, with the upper layers defined in 2005.

DVB-H (Digital Video Broadcast Handheld) is based on the very successful DVB-T (Digital Video Broadcast Terrestrial) standard that is now used in many countries for domestic digital television broadcasts. DVB-H has taken the basic standard and adapted so that it is suitable for use in a mobile environment, particularly with the electronics incorporated into a mobile phone.

The DVB-H standard like DVB-T uses a form of transmission called Orthogonal Frequency Division Multiplex (OFDM). This has been adopted because of its high data capacity and suitability for applications such as broadcasting. It also offers a high resilience to interference, can tolerate multi-path effects and is able to offer the possibility of a single frequency network, SFN.

"Note on OFDM:

Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each another there is no mutual interference. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. This means that when the signals are demodulated they will have a whole number of cycles in the symbol period and their contribution will sum to zero - in other words there is no interference contribution. The data to be transmitted is split across all the carriers and this means that by using error correction techniques, if some of the carriers are lost due to multi-path effects, then the data can be reconstructed. Additionally having data carried at a low rate across all the carriers means that the effects of reflections and inter-symbol interference can be overcome. It also means that single frequency networks, where all transmitters can transmit on the same channel can be implemented. Further information on OFDM can be found on this site under the Cellular telecoms section or by using the Search facility."

There are a variety of modes in which the DVB-H signal can be configured. These are conform to the same concepts as those used by DVB-T. These are 2K, 4K, and 8K modes, each having a different number of carriers as defined in the table below. The 4K mode is a further introduction beyond that which is available for DVB-T.


Parameter 2K mode 4K mode 8K mode
Number of active carriers 1705 3409 6817
Number of data carriers 1512 3024 6048
Individual carrier spacing 4464 Hz 2232 Hz 1116 Hz
Channel width 7.61 MHz 7.61 MHz 7.61 MHz

Signal parameters for DVB-H OFDM Signal (8MHz Channel)



The different modes balance the different requirements for network design, trading mobility for single frequency network size, with the 4K mode being that which is expected to be most widely used.

The standard will support a variety of different types of modulation within the OFDM signal. QPSK (Quadrature Phase Shift Keying), 16QAM (16 point Quadrature Amplitude Modulation), and 64QAM (64 point Quadrature Amplitude Modulation) will all be supported, chipsets being able to detect the modulation and receive the incoming signal. The choice of modulation is again a balance, QPSK offering the best reception under low signal and high noise conditions, but offering the lowest data rate. 64QAM offers the highest data rate, but requires the highest signal level to provide sufficiently error free reception.

Time slicing
One of the key requirements for any mobile TV system is that it should not give rise to undue battery drain. Mobile handset users are used to battery life times extending over several days, and although battery technology is improving, the basic mobile TV technology should ensure that battery drain is minimised.

There is a module within the standard and hence the software that enables the receiver to decode only the required service and shut off during the other service bits. It operates in such a way that it enables the receiver power consumption to be reduced while also offering an uninterrupted service for the required functions.

The time slicing elements of DVB-H enable the power consumption of the mobile TV receiver to be reduced by 90% when compared to a system not using this technique. Although the receiver will add some additional power drain on the battery, this will not be nearly as much as it would have been had the TV reception scheme not employed the time slicing techniques.

Interleaving
Interleaving is a technique where sequential data words or packets are spread across several transmitted data bursts. In this way, if one transmitted burst or group is lost as a result of noise or some other drop-out, then only a small proportion of the data in each original word or packet is lost and it can be reconstructed using the error detection and correction techniques employed.

Further levels of interleaving have been introduced into DVB-H beyond those used for DVB-T. The basic mode of interleaving used on DVB-T and which is also available for DVB-H is a native interleaver that interleaves bits over one OFDM symbol. However DVB-H provides a more in-depth interleaver that interleaves bits over two OFDM symbols (for the 4K mode) and four bits (for the 2K mode).

Using the in-depth interleaver enables the noise resilience performance of the 2K and 4K modes to be brought up to the performance of the 8K mode and it also improves the robustness of the reception of the transmissions in a mobile environment.

MPE-FEC
In view of the particularly difficult reception conditions that may occur in the mobile environment, further error correction schemes are included. A scheme known as MPE-FEC provides additional error correction to that applied in the physical layer by the interleaving. Tjis is a forward error correction scheme that is applied to the transmitted data and after reception and demodulation, allows the errors to be detected and corrected.

Compatibility with DVB-T
DVB-H is a development of DVB-T and as a result it shares many common components. It has also been designed so that it can be used in 6, 7, and 8 MHz channel schemes although the 8MHz scheme will be the most widely used. There is also a 5MHz option that may be used for non-broadcast applications.

In view of the similarities between DVB-H and DVB-T it is possible for both forms of transmission to exist together on the same multiplex. In this way a broadcaster may choose to run two DVB-T services and one DVB-H service on the same multiplex. This feature may be particularly attractive in the early days of DVB-H when separate spectrum is not available.


DVB-H has been used in a number of trials and appear to perform well. It ahs support from a number of the major industry players and is likely to achieve a considerable degree of acceptance world-wide. Accordingly it is likely to be one of the major standards, if not the major standard used for mobile video. Read more....!

Mobile video for cell phones promises to be a major force in the broadcasting and cellular industries over the coming years. With the functionality in phones increasing, along with people's expectations, placing mobile video or TV into a phone enables its use to be maximized.

Advantages of broadcast
The concept of broadcasting offers many advantages for mobile video applications. Using the mobile phone infrastructure has many advantages it is what may be termed a one to one communications system. However the costs of downloading videos will need to be paid by the user, and therefore may be large. If a broadcast style model is used, which may be thought of as a one to many communications link, then the delivery costs are much lower. The disadvantage is that the level of choice is reduced to what is being broadcast and there is no interactive operation. Nevertheless it is this business model that looks the more attractive and the one that will succeed for video and general mobile content. The high data rates of 3G being reserved for content such as data downloads, data communications, video conferencing and the like.

Business models
The exact way in which mobile video will be implemented as far as revenue is concerned will depend on the operators. There may be subscription services and there may also be services that are supported by advertising. The huge advantage that placing video onto mobile phones is that they are an accessory that is already in people's pockets. It is then possible to extend their functionality to include video, and this means that another unit is not required for this functionality. Additionally the billing infrastructure is already in place, so this too can be extended without the need to start again.

It is possible that the mobile video transmissions could also be used for other services. These could include traffic and weather reports that could be broadcast in the background and brought up as required on the mobile. Additionally they could be used for software upgrades. In this way mobiles could be upgraded online, and new features added if necessary.

Spectrum considerations
One of the big issues surrounding the mobile video transmissions is that of radio spectrum. As these transmissions will not utilize the bands already allocated for cellular communications, further bandwidth will be needed. This is likely to delay the introduction of mobile video services in some countries.

In an ideal world it would be advantageous to allocate the same bands for mobile video broadcasting worldwide. In reality this is unlikely to happen totally, although there will undoubtedly be a large degree of commonality, although it is likely that not all countries will be able to adopt the same bands. In addition to this there are no bands set aside for DVB-H broadcasting, although for DMB, the technology is sufficiently similar to utilize the bands allocated for broadcasting using DAB.

For the long term it is anticipated that as the UHF analogue transmissions are closed this will release vast amounts of valuable spectrum and some of this could be allocated to mobile video broadcasts and in particular for DVB-H that ahs no allocations that can currently be used.

Main systems
As might be expected, there are several systems being developed. Around the world there are four major standards that are appearing, two of which appear to be open international standards.

* T-DMB Terrestrial Digital Multimedia Broadcasting

* DVB-H Digitla Multimedia Broadcasting Handheld

* ISDB-T Integrated Services Digital Broadcasting Terrestrial

* MediaFLO

Of these T-DMB is based on the DAB system that is currently gaining significant support in the UK and other countries around the world for audio broadcasting. DVB-H is based upon the DVB-T terrestrial television broadcasting system that is used in the UK and many other countries. ISDB-T is a standard that is only being used in Japan, and finally Mediaflow is a scheme that is being developed by Qualcomm. Mediaflow is a registered trade name of Qualcomm

System comparisons
It is worth looking at the comparisons between the various systems that are being trialled and utilized for downloading video.



A number of trials of both DMB and DVB-H have taken place in a number of countries around the globe. It appears that in the future both systems may be used, and additionally a variety of different frequency bands may be used. To combat this and enable phones to provide mobile video roaming, some manufacturers are developing multi-band multi-standard chipsets. Although the risk is that these will consume more battery power, careful design has ensured that this may not be the case. Read more....!

i-mode (imode) is the platform for mobile phone communications that has had an astounding success in Japan. Now the company that launched the system in February 1999, NTT DoCoMo, is launching other i-mode cell phone systems in other countries around the world.

i-mode is an information service, and this give rise to its name. It is provided as a premium add-on service to the basic cellular phone system and provides many facilities including e-mail, internet surfing, and picture mailing. Requiring special i-mode terminals to be purchased by the user, the system operates as a packet based network overlaid on the basic cellular system.

i-mail
One of the most popular aspects of the i-mode service is i-mail that enables users to send e-mail messages to others on the same service, or to anyone with an e-mail account.

There are limits to the number of characters that can be sent and received, but these are much greater than the limits that apply to the SMS service that has become so popular on GSM. For i-mode users can send messages up to 500 characters in length and can receive up to 4000 characters.

On opening an i-mode account, users are given an e-mail address that consists of a random mix of characters. This can be changed once the account has been set up to personalise it for the user, and to make it more memorable.

Internet access
The other major element of i-mode is its ability to surf the internet and access internet sites. Specially developed websites using a cut down version of HTML known as cHTML is used to enable sites to be downloaded more quickly whilst providing content that can be satisfactorily viewed on the phones. The i-mode menu on the phone enables the user to select one of four zones: namely Lifestyle (for sports, weather local events etc); Transaction (for facilities including banking, shopping, credit card information and the like); Database (for services including traffic updates, TV and radio schedules as well as cinema information); and Entertainment (where games and music downloads are available along with screen savers, ring tones and hobby information).

One of the major incentives to the development of the special i-mode sites is that the operators have been investing in the content developers to develop official i-mode sites. Rather than splitting the revenues 50/50 as in the case of other similar systems, a revenue share of 90/10 in favour of the content developer has been adopted. This has stimulated a healthy growth and there are many thousands of official i-mode sites, with countless thousands more unofficial ones that are i-mode compatible. This means that the user has a great degree of choice and the usage has risen. In this way the operator has been able to see considerably increased revenues.

On top of these services there is i-shot for taking and sending pictures as well as i-appli for running applications such as downloaded games, and i-area for location based services.

The System
The i-mode system was originally run on the PDC system that is found in Japan, however it can also be applied to other cellular systems as well.

Based on a packet transmission to the mobile phones, i-mode uses a protocol known as PDC-P (Personal Digital Cellular Packet) for the interchange of data packets. The service is based on a 3 channel TDMA model to provide a common access system that can be shared by multiple users on a random access basis. Using multi-slot transmissions across the three channels data speeds of up to 28.8 kbps can be achieved.

CDMA2000 1X is widespread in Japan, and i-mode system is also used with this system. As data speeds are very much higher for 1X, this enables faster and easier access of the data. Services are also available on the faster data only CDMA2000 1xEV-DO system that enables data transfer at rates up to 2.4 Mbps.


The future of i-mode looks bright. While it may have been originally seen as a rising sun in the East, it is now appearing in many countries and competing with other technologies and systems. Read more....!

This final page of the UMTS / WCDMA tutorial looks at three elements of the system, namely the way packet data is carried, the way speech coding is accomplished and handover, including hard, soft and softer handover.

Packet data
Packet data is an increasingly important element within mobile phone applications. WCDMA is able to carry data in this format in two ways. The first is for short data packets to be appended directly to a random access burst. This method is called common channel packet transmission and it is used for short infrequent packets. It is preferable to transmit short packets in this manner because the link maintenance needed for a dedicated channel would lead to an unacceptable overhead. Additionally the delay in setting up a packet data channel and transferring the operational mode to this format is avoided.

Larger or more frequent packets have to be transmitted on a dedicated channel. A large single packet is transmitted using a single-packet scheme where the dedicated channel is released immediately after the packet has been transmitted. In a multipacket scheme the dedicated channel is maintained by transmitting power control and synchronization information between subsequent packets.

Speech coding
Speech coding in UMTS uses a variety of source rates. As a result, a variety of vocoders are employed including the GSM EFR vocoder. When a variety of rates are available, a system known as Adaptive Multi-Rate (AMR) may be employed where rate is chosen according to the system capacity and requirements. This scheme is the same as that used on GSM. The actual vocoder that is chosen is governed by the system.

The speech coding process can be combined with a voice activity detector. This is particularly useful because during normal conversations there are long periods of inactivity. In the same way that discontinuous transmission is applied to GSM, the same is also true for UMTS. It employs the same technique of inserting background noise when there is no speech as when the discontinuous transmission cuts out the transmission no background noise would otherwise be heard and this can be very disconcerting for the listener.

Discontinuous reception
One of the big issues with mobile phones in general is that of battery life. It is one of the key differentiators that people take into account when buying a phone and this gives a measure of its importance. Taking this into consideration when developing the UMTS / WCDMA standard a discontinuous reception or sleep mode was introduced. This mode allows several non-essential segments of the phone circuitry to power down during periods when paging messages will not be received.

To enable this facility to be introduced into the UMTS UE circuitry the paging channel is divided into groups or subchannels. The actual number of the paging subchannel to be used by a particular UE is assigned by the network. In this way the UE only has to listen for part of the time. To achieve this the Paging Indicator Channel (PICH) is split into 10 ms frames, each of which comprises 300 bits - 288 for paging data and 12 idle bits. At the beginning of each paging channel frame there is a Paging Indicator (PI) that identifies the paging group being transmitted. By synchronising with the paging channels being transmitted it is able to turn the receiver on only when it needs to monitor the paging channel. As the receiver, with its RF circuitry, will consume power, savings can be made by switching it off.

Handover
Within UMTS, handover follows many of the similar concepts to those used for other CDMA systems. There are three basic types of handover: hard, soft and softer. All three types are used but under different circumstances.

Hard handover is like that used for the previous generations of systems. Here, as the UE moves out of range of one node B, the call has to be handed over to another frequency channel. In this instance simultaneous reception of both channels is not possible and there must be a physical break.

Soft handover is a technique that was not available on the previous generations of mobile phone systems. With CDMA systems it is possible to have adjacent cell sites on the same frequency, and as a result it is possible for the UE to receive the signals from two adjacent cells at once, and they are also able to receive the signals from the UE. When this occurs and handover is affected it is known as soft handover.

The decisions about handover are generally handled by the RNC. It continually monitors information regarding the signals being received by both the UE and node B and when a particular link has fallen below a given level and another better radio channel is available, it initiates a handover. As part of this monitoring process, the UE measures the Received Signal Code Power (RSCP) and Received Signal Strength Indicator (RSSI) and the information is then returned to the node B and hence to the RNC on the uplink control channel.

If a hard handover is required then the RNC will instruct the UE to adopt a compressed mode, allowing short time intervals in which the UE is able to measure the channel quality of other radio channels. Read more....!

The data carried by the UMTS / WCDMA transmissions is organised into frames, slots and channels. In this way all the payload data as well as the control data can be carried in an efficient manner.

UMTS uses CDMA techniques (as WCDMA) as its multiple access technology, but it additionally uses time division techniques with a slot and frame structure to provide the full channel structure.

A channel is divided into 10 ms frames, each of which has fifteen time slots each of 666 microseconds length. On the downlink the time is further subdivided so that the time slots contain fields that contain either user data or control messages.

On the uplink dual channel modulation is used so that both data and control are transmitted simultaneously. Here the control elements contain a pilot signal, Transport Format Combination Identifier (TFCI), FeedBack Information (FBI) and Transmission Power Control (TPC).

The channels carried are categorised into three: logical, transport and physical channels. The logical channels define the way in which the data will be transferred, the transport channel along with the logical channel again defines the way in which the data is transferred, the physical channel carries the payload data and govern the physical characteristics of the signal.

The channels are organised such that the logical channels are related to what is transported, whereas the physical layer transport channels deal with how, and with what characteristics. The MAC layer provides data transfer services on logical channels. A set of logical channel types is defined for different kinds of data transfer services.

Logical Channels:

Broadcast Control Channel (BCCH), (downlink). This channel broadcasts information to UEs relevant to the cell, such as radio channels of neighbouring cells, etc.

Paging Control Channel (PCCH), (downlink). This channel is associated with the PICH and is used for paging messages and notification information.

Dedicated Control Channel (DCCH), (up and downlinks) This channel is used to carry dedicated control information in both directions.

Common Control Channel (CCCH), (up and downlinks). This bi-directional channel is used to transfer control information.

Shared Channel Control Channel (SHCCH), (bi-directional). This channel is bi-directional and only found in the TDD form of WCDMA / UMTS, where it is used to transport shared channel control information.

Dedicated Traffic Channel (DTCH), (up and downlinks). This is a bidirectional channel used to carry user data or traffic.

Common Traffic Channel (CTCH), (downlink) A unidirectional channel used to transfer dedicated user information to a group of UEs.

Transport Channels:

Dedicated Transport Channel (DCH), (up and downlink). This is used to transfer data to a particular UE. Each UE has its own DCH in each direction.

Broadcast Channel (BCH), (downlink). This channel broadcasts information to the UEs in the cell to enable them to identify the network and the cell.

Forward Access Channel (FACH),(down link). This is channel carries data or information to the UEs that are registered on the system. There may be more than one FACH per cell as they may carry packet data.

Paging Channel (PCH) (downlink). This channel carries messages that alert the UE to incoming calls, SMS messages, data sessions or required maintenance such as re-registration.

Random Access Channel (RACH), (uplink). This channel carries requests for service from UEs trying to access the system

Uplink Common Packet Channel (CPCH), (uplink). This channel provides additional capability beyond that of the RACH and for fast power control.

Downlink Shared Channel (DSCH) (downlink).This channel can be shared by several users and is used for data that is "bursty" in nature such as that obtained from web browsing etc.

Physical Channels:

Primary Common Control Physical Channel (PCCPCH) (downlink). This channel continuously broadcasts system identification and access control information.

Secondary Common Control Physical Channel (SCCPCH) (downlink) This channel carries the Forward Access Channel (FACH) providing control information, and the Paging Channel (PACH) with messages for UEs that are registered on the network.

Physical Random Access Channel (PRACH) (uplink). This channel enables the UE to transmit random access bursts in an attempt to access a network.

Dedicated Physical Data Channel (DPDCH) (up and downlink). This channel is used to transfer user data.

Dedicated Physical Control Channel (DPCCH) (up and downlink). This channel carries control information to and from the UE. In both directions the channel carries pilot bits and the Transport Format Combination Identifier (TFCI). The downlink channel also includes the Transmit Power Control and FeedBack Information (FBI) bits.

Physical Downlink Shared Channel (PDSCH) (downlink). This channel shares control information to UEs within the coverage area of the node B.

Physical Common Packet Channel (PCPCH). This channel is specifically intended to carry packet data. In operation the UE monitors the system to check if it is busy, and if not it then transmits a brief access burst. This is retransmitted if no acknowledgement is gained with a slight increase in power each time. Once the node B acknowledges the request, the data is transmitted on the channel.

Synchronisation Channel (SCH) The synchronisation channel is used in allowing UEs to synchronise with the network.

Common Pilot Channel (CPICH) This channel is transmitted by every node B so that the UEs are able estimate the timing for signal demodulation. Additionally they can be used as a beacon for the UE to determine the best cell with which to communicate.

Acquisition Indicator Channel (AICH) The AICH is used to inform a UE about the Data Channel (DCH) it can use to communicate with the node B. This channel assignment occurs as a result of a successful random access service request from the UE.

Paging Indication Channel (PICH) This channel provides the information to the UE to be able to operate its sleep mode to conserve its battery when listening on the Paging Channel (PCH). As the UE needs to know when to monitor the PCH, data is provided on the PICH to assign a UE a paging repetition ratio to enable it to determine how often it needs to 'wake up' and listen to the PCH.

CPCH Status Indication Channel (CSICH) This channel, which only appears in the downlink carries the status of the CPCH and may also be used to carry some intermittent, or "bursty" data. It works in a similar fashion to PICH.

Collision Detection/Channel Assignment Indication Channel (CD/CA-ICH) This channel, present in the downlink is used to indicate whether the channel assignment is active or inactive to the UE. Read more....!

Physical layer within UMTS / WCDMA is totally different to that employed by GSM. It employs a spread spectrum transmission in the form of CDMA rather than the TDMA transmissions used for GSM. Additionally it currently uses different frequencies to those allocated for GSM.

Frequencies
There are currently six bands that are specified for use for UMTS / WCDMA although operation on other frequencies is not precluded. However much of the focus for UMTS is currently on frequency allocations around 2 GHz. At the World Administrative radio Conference in 1992, the bands 1885 - 2025 and 2110 - 2200 MHz were set aside for use on a world wide basis by administrations wishing to implement International Mobile Telecommunications-2000 (IMT-2000). The aim was that allocating spectrum on a world wide basis would facilitate easy roaming for UMTS / WCDMA users.

Within these bands the portions have been reserved for different uses:

* 1920-1980 and 2110-2170 MHz Frequency Division Duplex (FDD, W-CDMA) Paired uplink and downlink, channel spacing is 5 MHz and raster is 200 kHz. An Operator needs 3 - 4 channels (2x15 MHz or 2x20 MHz) to be able to build a high-speed, high-capacity network.

* 1900-1920 and 2010-2025 MHz Time Division Duplex (TDD, TD/CDMA) Unpaired, channel spacing is 5 MHz and raster is 200 kHz. Transmit and receive transmissions are not separated in frequency.

* 1980-2010 and 2170-2200 MHz Satellite uplink and downlink.

Carrier frequencies are designated by a UTRA Absolute Radio Frequency Channel Number (UARFCN). This can be calculated from:

UARFCN = 5 x (frequency in MHz)

UMTS uses wideband CDMA as the radio transport mechanism. The channels are spaced by 5 MHz. The modulation that is used is different on the uplink and downlink. The downlink uses quadrature phase shift keying (QPSK) for all transport channels. However the uplink uses two separate channels so that the cycling of the transmitter on and off does not cause interference on the audio lines, a problem that was experienced on GSM. The dual channels (dual channel phase shift keying) are achieved by applying the coded user data to the I or In-phase input to the DQPSK modulator, and control data which has been encoded using a different code to the Q or quadrature input to the modulator.

Spreading
The data to be transmitted is encoded using a spreading code particular to a given user. In this way only the desired recipient is able to correlate and decode the signal, all other signals appearing as noise. This allows the physical RF channel to be used by several users simultaneously.

The data of a CDMA signal is multiplied with a chip or spreading code to increase the bandwidth of the signal. For WCDMA, each physical channel is spread with a unique and variable spreading sequence. The overall degree of spreading varies to enable the final signal to fill the required channel bandwidth. As the input data rate may vary from one application to the next, so the degree of spreading needs to be varied accordingly.

For the downlink the transmitted symbol rate is 3.84 M symbols per second. As the form of modulation used is QPSK this enables two bits of information to be transmitted for every symbol, thereby enabling a maximum data rate of twice the symbol rate or 7.68 Mbps. Therefore if the actual rate of the data to be transmitted is 15 kbps then a spreading factor of 512 is required to bring the signal up to the required chip rate for transmission in the required bandwidth. If the data to be carried has a higher data rate then a lower spreading rate is required to balance this out. It is worth remembering that altering the chip rate does alter the processing gain of the overall system and this needs to be accommodated in the signal processing as well. Higher spreading factors are more easily correlated by the receiver and therefore a lower transmit power can be used for the same symbol error rate.

The codes required to spread the signal must be orthogonal if they are to enable multiple users and channels to operate without mutual interference. The codes used in W-CDMA are Orthogonal Variable Spreading Factor (OVSF) codes, and they must remain synchronous to operate. As it is not possible to retain exact synchronisation for this, a second set of scrambling codes is used to ensure that interference does not result. This scrambling code is a pseudo random number (PN) code. Thus there are two stages of spreading. The first using the OSVF code and the second using a scrambling PN code. These codes are used to provide different levels of separation. The OVSF spreading codes are used to identify the user services in the uplink and user channels in the downlink whereas the PN code is used to identify the individual node B or UE.

On the uplink there is a choice of millions of different PN codes. These are processed to include a masked individual code to identify the UE. As a result there are more than sufficient codes to accommodate the number of different UEs likely to access a network. For the downlink a short code is used. There are a total of 512 different codes that can be used, one of which will be assigned to each node B.

Synchronisation
The level of synchronisation required for the WCDMA system to operate is provided from the Primary Synchronisation Channel (P-SCH) and the Secondary Synchronisation Channel (S-SCH). These channels are treated in a different manner to the normal channels and as a result they are not spread using the OVSFs and PN codes. Instead they are spread using synchronisation codes. There are two types that are used. The first is called the primary code and is used on the P-SCH, and the second is named a secondary code and is used on the S-SCH.

The primary code is the same for all cells and is a 256 chip sequence that is transmitted during the first 256 chips of each time slot. This allows the UE to synchronise with the base station for the time slot.

Once the UE has gained time slot synchronisation it only knows the start and stop of the time slot, but it does not know information about the particular time slot, or the frame. This is gained using the secondary synchronisation codes.

There is a total of sixteen different secondary synchronisation codes. One code is sent at the beginning of the time slot, i.e. the first 256 chips. It consists of 15 synchronisation codes and there are 64 different scrambling code groups. When received, the UE is able to determine before which synchronisation code the overall frame begins. In this way the UE is able to gain complete synchronisation.

The scrambling codes in the S-SCH also enable the UE to identify which scrambling code is being used and hence it can identify the base station. The scrambling codes are divided into 64 code groups, each having eight codes. This means that after achieving frame synchronisation, the UE only has a choice of one in eight codes and it can therefore try to decode the CPICH channel. Once it has achieved this it is able to read the BCH information and achieve better timing and it is able to monitor the P-CCPCH.

Power Control
As with any CDMA system it is essential that the base station receives all the UEs at approximately the same power level. If not, the UEs that are further away will be lower in strength than those closer to the node B and they will not be heard. This effect is often referred to as the near-far effect. To overcome this the node B instructs those stations closer in, to reduce their transmitted power, and those further away to increase theirs. In this way all stations will be received at approximately the same strength.

It is also important for node Bs to control their power levels effectively. As the signals transmitted by the different node Bs are not orthogonal to one another it is possible that signals from different ones will interfere. Accordingly their power is also kept to the minimum required by the UEs being served.

To achieve the power control there are two techniques that are employed: open loop; and closed loop.

Open loop techniques are used during the initial access before communication between the UE and node B has been fully established. It simply operates by making a measurement of the received signal strength and thereby estimating the transmitter power required. As the transmit and receive frequencies are different, the path losses in either direction will be different and therefore this method cannot be any more than a good estimate.

Once the UE has accessed the system and is in communication with the node B, closed loop techniques are used. A measurement of the signal strength is taken in each time slot. As a result of this a power control bit is sent requesting the power to be stepped up or down. This process is undertaken on both the up and downlinks. The fact that only one bit is assigned to power control means that the power will be continually changing. Once it has reached approximately the right level then it would step up and then down by one level. In practice the position of the mobile would change, or the path would change as a result of other movements and this would cause the signal level to move, so the continual change is not a problem. Read more....!

UMTS TDD (Universal mobile telecommunications system - time division duplex) is a growing standard. Although UMTS TDD is not as widely deployed as the more popular UMTS FDD which is being deployed for the 3G mobile phone systems, UMTS TDD is nevertheless being used and providing a viable service for many applications. In particular it is being used to provide mobile broadband data services, and other applications may include its use in providing mobile TV applications.

TDD - time division duplex
A communications system requires that communication is possible in both directions: to and from the base station to the remote station. There are a number of ways in which this can be achieved. The most obvious is to transmit on one frequency and receive on another. The frequency difference between the two transmissions being such that the two signals do not interfere. This is known as frequency division duplex (FDD) and it is one of the most commonly used schemes, and it is used by most cellular schemes.

It is also possible to use a single frequency and rather than using different frequency allocations, use different time allocations. If the transmission times are split into slots, then transmissions in one direction take place in one time slot, and those in the other direction take place in another. It is this scheme that is known as time division duplex, TDD, and it is used for UMTS-TDD.

One of the major advantages of TDD systems such as UMTS TDD is that it is possible to vary the capacity in either direction. By altering the proportion of time allocated for transmission in each direction (downlink and uplink) it is possible to enable it to match the traffic load in each direction.

Typically there is more traffic in the downlink (network to the mobile) than in the uplink (mobile to network). Accordingly the operator is able to allocate more time to the downlink transmission than the uplink. This is not possible with the paired spectrum required for FDD systems where it is not possible to re-allocate the use of the different bands. As a result of this, it is possible to make very efficient use of the available spectrum.

UMTS TDD within 3GPP
Al the standards for UMTS 3G systems have been defined under the auspices of 3GPP - the third generation partnership project. The standards not only define the FDD systems, but also the TDD system.

In these specifications, it was the original intent of UMTS that the TDD spectrum would be used to provide high data rates in selected areas forming what could be termed 3G hot zones.

UMTS TDD details
UMTS TDD uses many of the same basic parameters as UMTS FDD. The same 5 MHz channel bandwidths are used. UMTS TDD also uses direct sequence spread spectrum and different users and what can be termed "logical channels" are separated using different spreading codes. Only when the receiver uses the same code in the correlation process, is the data recovered. In W-CDMA all other logical channels using different spreading codes appear as noise on the channel and ultimately limit the capacity of the system. In UMTS TDD, a scheme known as multi user detection (MUD) is employed in the receiver and improves the removal of the interfering codes, allowing higher data rates and capacity.

In addition to the separation of users by using different logical channels as a result of the different spreading codes, further separation between users may be provided by allocating different time slots. There are 15 time slots in UMTS TDD. Of these, three are used for overhead such as signalling, etc and this leaves twelve time slots for user traffic. In each timeslot there can be 16 codes. Capacity is allocated to users on demand, using a two dimensional matrix of timeslots and codes.

In order for UMTS TDD to achieve the best overall performance, the transport format, i.e. the modulation and forward error correction can be altered for each user. The schemes are chosen by the network, and will depend on the signal characteristics in both directions. Higher order forms of modulation enable higher data speeds to be accommodated, but they are less resilient to noise and interference, and this means that the higher data rate modulation schemes are only used when signal strengths are high. Additionally the levels of forward error correction can be changed. When errors are likely, i.e. when signal strengths are low or interference levels are high, Similarly higher levels of forward error correction are needed under low require additional data to be sent and this slows the payload transfer rate. Thus it is possible to achieve much higher data transfer rates when signals are strong and interference levels are low.

Spectrum allocations
Standard allocations of radio spectrum have been made for 3G telecommunications systems in most countries around the globe. In Europe and many other areas spectrum has been allocated for UMTS FDD between 1920MHz to 1980MHz and 2110MHz to 2170MHz. For UMTS TDD spectrum is primarily located between 1900MHz and 1920MHz and between 2010MHz and 2025MHz. In addition to this there are some other allocations around 3 GHz.

UMTS TDD performance
UMTS TDD is able to support high peak data rates. Release 5 of the UMTS standard provides HSDPA (high-speed downlink packet access). The scheme allows the use of a higher order modulation scheme called 16-QAM (16 point quadrature amplitude modulation), which enables peak rates of 10 Mbps per sector in commercial deployments. The next release increases the modulation to 64-QAM, and introduces intercell interference cancellation (called Generalized MUD) and MIMO (multiple in, multiple out). In combination, these increase the peak rate to 31 Mbps per sector.

Future
UMTS TDD, while not as widely deployed as UMTS FDD nevertheless offers significant advantages for a number of applications. While currently being used for mobile broadband, it appears as if it could serve to provide mobile TV, and other data in a filed where new methods of transport are being sought. Read more....!

Work is now staring on developing the standards for High Speed Uplink Packet Access ( HSUPA ) to improve the data rates on the 3G W-CDMA mobile or cell phone standard. With the cellular telecommunications standards established and work progressing to introduce the equipment for High Speed Downlink Packet Access ( HSDPA ), the standards are now starting to be developed to enable the uplink from the mobile handset or User Equipment (UE) to the base station (Node B) to be able to handle data at similar speeds. This is known as HSUPA and it will enable new features including full video conferencing to be introduced.

For most applications including internet surfing, emails, video downloads and the like, data flowing in the downlink is far greater than the uplink. However for applications such as video conferencing, data flows equally in both directions. It is anticipated that video conferencing will become an increasing requirement, and a significant revenue generator for the operators in the near future. To enable high quality video to be passed, it is therefore essential to ensure that the uplink performs as fast as the downlink.

Although it is very early days for the standards, work on HSUPA has already started under the auspices of 3GPP, the body that controls the Wideband CDMA (W-CDMA) standards.

Technologies used
It is anticipated that many of the same techniques used in HSDPA will be used for HSUPA, but these still need to be formalised. Accordingly it is expected that adaptive modulation, along with HARQ (hybrid automatic repeat request) will be used. Improvements in the base station similar to those employed on HSDPA are also likely.

Originally W-CDMA had used only QPSK as the modulation scheme, however under the new HSUPA system,16-QAM which can carry a higher data rate, but is less resilient to noise is also used when the link is sufficiently robust. The robustness of the channel and its suitability to use 16-QAM instead of QPSK is determined by analysing information fed back about a variety of parameters. These include details of the channel physical layer conditions, power control, Quality of Service (QoS), and information specific to HSDPA.

Fast HARQ (hybrid automatic repeat request), has also been implemented along with multi-code operation and this eliminates the need for a variable spreading factor. By using these approaches all users, whether near or far from the base station are able to receive the optimum available data rate.

It is also likely that within the HSUPA upgrades there will be an additional uplink data channel introduced comparable to that in the downlink.

The future
Many manufacturers are working on implementing HSDPA, with initial equipment deliveries anticipated in 2005. Now with HSUPA in people's sights this should be implemented in the following years, making a far faster 3G system than is currently available. Read more....!

Improvements and enhancements are being made to the Wideband CDMA or UMTS 3G telecommunications system. Called High Speed Downlink Packet Access ( HSDPA ) the new technology promises to increase the download data rate five fold. In addition to this HSDPA also provides a two fold increase in base station capacity.

The introduction of HSDPA technology has come about as a result of the need to drive down costs as well as increasing the data rates possible. Current trends show the volume of packet switched data rising and overtaking the more traditional circuit switched traffic. By adopting a packet based approach to the delivery of digital content as well as IP based person to person digitized voice, a single session can be used for multiple purposes and this can be used to drive revenues upwards. With this approach in mind the use of HSDPA is a key element in providing the user with a better service as well as increasing revenues as a result of increased capacity and usage for the service providers.

Standards
The new high speed technology part of the W-CDMA evolution. Release 4 of the 3GPP W-CDMA standard provided the efficient IP support to enable provision of services through an all IP core network. Then Release 5 included HSDPA itself with support for the packet-based multimedia services. A further enhancement known as MIMO (Multiple Input Multiple Output) will then be contained within Release 6. As HSDPA needs to work alongside the original Release 99 systems, the new technology is completely backwards compatible.

Key technologies
One of the keys to the operation of HSDPA is the use of an additional form of modulation. Originally W-CDMA had used only QPSK as the modulation scheme, however under the new system16-QAM which can carry a higher data rate, but is less resilient to noise is also used when the link is sufficiently robust. The robustness of the channel and its suitability to use 16-QAM instead of QPSK is determined by analyzing information fed back about a variety of parameters. These include details of the channel physical layer conditions, power control, Quality of Service (QoS), and information specific to HSDPA.

Fast HARQ (hybrid automatic repeat request), has also been implemented along with multi-code operation and this eliminates the need for a variable spreading factor. By using these approaches all users, whether near or far from the base station are able to receive the optimum available data rate.

Further advances have been made in the area of scheduling. By moving more intelligence into the base station, data traffic scheduling can be achieved in a more dynamic fashion. This enables variations arising from fast fading can be accommodated and the cell is even able to allocate much of the cell capacity for a short period of time to a particular user. In this way the user is able to receive the data as fast as conditions allow.

A further channel known as the High Speed Downlink Shared Channel (HS-DSCH) has been introduced. W-CDMA normally carries data over dedicated transport channels (DCHs), several of which are multiplexed onto one RF carrier. This approach has been adopted because it provides the optimum performance with continuous user data. Under the new scheme the "bursty" nature of the data has been accounted for and more efficient use of the available spectrum has been made.

Performance
Using the new HSDPA scheme it will be possible to achieve peak data rates of 10 Mbps within the 5 MHz channel bandwidth offered under W-CDMA. The new scheme has a number of benefits. It improves the overall network packet data capacity, improves the spectral efficiency and will enable networks to achieve a lower delivery cost per bit. Users will see higher data speeds as well as shorter service response times and better availability of services. However new mobile designs will need to be able to handle the increased data throughput rates. Reports indicate that handsets will need to have at least double the memory currently contained within handsets. Nevertheless the advantages of HSDPA mean that it will be widely used as networks are upgraded and new phones introduced. Read more....!